Prop difference

Tyler Mitchem

Tyler Mitchem

Filing Flight Plan
Joined
Apr 2, 2017
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chicago
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Display name:
Tyler
Whats the difference between a two blade prop and a three blade prop
 
1) the number of blades ;)
2) the diameter is smaller usually on 3 blades
3) 3 blades better for climb
4) 2 blades have a slight cruise speed advantage
5) 3 blades are quieter
6) 3 blades look better
 
2 Blade is lighter, cheaper, faster, and better looking.

3 blade is good on a Cessna 185 floatplane to get on the step. After that, it is a drag.
 
SkyDog58 said:
A better question would be what are the advantages and disadvantages between the two.
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@Radar Contact gave the bullet points well above, although I'd point out that the 3-bladed being quieter is contingent upon a smaller prop diameter.

Really you have to look at the particular props being used. We put MT 4-bladers on the 414 last year and there's a noticeable performance improvement all around, but they also have a modern blade design in addition to the differences in diameter, etc. So they are faster in cruise while also having better takeoff and climb performance. I was also switching from 3-bladed McCauleys which were a really bad blade design.
 
Three blade props are used when diameter limitations (due to ground clearance or tip speed) mean a two blade prop can't efficiently absorb all of the engine's power. Three blades are inherently less efficient than two blades, but a properly sized 3 blade prop will do better than a too-small (due to diameter limitation) two blade prop.
 
I went from 230hp and 88" 2 blade to 275hp and 86" 3 blade. I'll never go back. 3 blades balance nicely on a 6 cylinder engine. Smoooooth.
 
Ted DuPuis said:
@Radar Contact gave the bullet points well above, although I'd point out that the 3-bladed being quieter is contingent upon a smaller prop diameter.

Really you have to look at the particular props being used. We put MT 4-bladers on the 414 last year and there's a noticeable performance improvement all around, but they also have a modern blade design in addition to the differences in diameter, etc. So they are faster in cruise while also having better takeoff and climb performance. I was also switching from 3-bladed McCauleys which were a really bad blade design.
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Ted, Do you have data to support that statement or is it anecdotal? Without data to support your claim it's like saying my second wife is better than the first one. :D
 
Norman said:
Ted, Do you have data to support that statement or is it anecdotal? Without data to support your claim it's like saying my second wife is better than the first one. :D
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Well, what sort of data are you looking for? True airspeed at FL190 I've seen a solid 6+ KTAS faster (was 194 KTAS before, now 200+). Climb rates are a solid 100-200 FPM improved for cruise climb at the same IAS. Takeoff performance is hard to tell on this plane, so we can call it a wash (although MT claims it's a few percent improved). This is all at the same power settings with similar loads and temperatures. They're also quieter - the kids can hear their iPads in the back without wearing headsets, which they weren't able to before.

If you're looking for a bunch of videos posted to YouTube then I don't have them, you'll just have to trust what I say or opt not to. I'll trust you that your 2nd wife is better. ;)
 
Used to love hearing our 185 on floats taking off with the 2 blade ... from way across town. She used to really bark!
 
What about 4 blades?
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:D
 
185 prop noise is a function of prop tip speed. The 185 max prop length is 86". 3 86" blades spinning at 2850 makes more noise than 2 blades at the same length and prop speed. And they pull harder, too. The unmentioned advantage of three blades is air braking. Get your prop governor set wrong and spin three 86" blades at 2900+? Even your friends don't wanna be around when you take off. ;)
 
Stewartb said:
185 prop noise is a function of prop tip speed. The 185 max prop length is 86". 3 86" blades spinning at 2850 makes more noise than 2 blades at the same length and prop speed. And they pull harder, too. The unmentioned advantage of three blades is air braking. Get your prop governor set wrong and spin three 86" blades at 2900+? Even your friends don't wanna be around when you take off. ;)
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The two bladed McCauley is about 6 inches longer and a flatter pitch. Which is why we used it on floats. All the others we had used three bladed props. Between the 185's and the 206's in our fleet, they made money hand over fist. Hardly any snags, full tanis heat, all engines made TBO, no maintenance shortcuts. We treated them right and they treated us well in return!
 
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